This project provides continued morphologic support for the identification and classification of microsporidia isolated in tissue culture and inoculated into Rhesus monkeys for development of an animal model. Morphologic characterization of Encephalitozoon hellem, a new microsporidian parasite isolated from the eyes of AIDS patients, has been introduced into SIV-infected monkeys. We anticipate that additional specimens from human and veterinary patients will be examined as the result of a collaboration with investigators at George Washington University Medical Center, Washington, D.C., Charity Hospital, and other sites. The range of microsporidia examined will expand to include ocular and enteric microsporidia. Electron microscopy is currently being used to evaluate effects of antiparasitic drugs in an infected cell culture system.